The present invention relates to thin film magnetic heads and more particularly to a thin film magnetic head suitable for a magnetic tape or magnetic disc memory device in which the magnetic head comes into contact with a recording medium.
With recent trend to increasing density of magnetic recording, popularity of the magnetic head is shifting from a conventional bulky monolithic type magnetic head to a thin film magnetic head having excellent high frequency characteristics.
FIG. 1 shows one example of a thin film magnetic head for use in a magnetic tape memory device. One substrate 1 formed with a thin film head element 2 opposes the other substrate 1 also formed with a thin film head element 2 with a magnetic shielding plate 3 interposed therebetween, and a resultant laminated assembly is clamped to a frame 4. For transmission and reception of signals, either thin film head element 2 is connected with lead conductors 5 formed on a flexible printed sheet. Because of a thin film structure, magnetic material of the thin film magnetic head is prone to magnetic saturation and the length of magnetic path cannot be increased. Therefore, the magnetic gap depth cannot be so large as that for the conventional head. In such a thin film magnetic head, there arises a problem that the tip portion of the magnetic head in contact with the recording medium tends to wear. Therefore, it has hitherto been proposed to use a highly wear-proof sintered member of Al.sub.2 O.sub.3.TiC as the substrate formed with the thin film head element.
However, this material disadvantageously has poor slidability against the recording medium and lacks reliability. It will therefore follow that with the use of the Al.sub.2 O.sub.3.TiC sintered member as the substrate 1 of FIG. 1, a portion of the substrate 1 forms a surface being in contact with the magnetic tape, thereby succeeding in suppressing wear of the magnetic head; whereas the poor slidability attended with sliding friction generates heat by which a magnetic tape binder is softened, with the result that the softened binder tends to adhere to the magnetic head by accident. This imposes a fatal problem on reliability.
A similar problem is encountered in the magnetic disc memory device. More particularly, with the increasing density of magnetic recording, the gap (flying height) between the magnetic disc and the magnetic head is so decreased that the magnetic head frequently comes into contact with the magnetic disc during sliding, resulting in tendency toward a trouble that is so-called head crash.
To eliminate these disadvantages, one measure adapted for the magnetic disc is to coat an air bearing surface of a slider with a highly lubricative material, and another measure also adapted for the magnetic disc is to impregnate a liquid lubricant in porous voids inherently formed in a sintered polycrystalline member standing for the slider. Many approaches to these measures have been proposed. For example, Japanese Patent Application Laid-open No. 111,166/81 proposes a method of embedding lap materials of, for example, Sn in the porous voids in the slider, Japanese Patent Application Laid-open No. 47,956/81 a method of impregnating fluorine resin in the porous voids in the slider, Japanese Patent Application Laid-open No. 107,326/81 a method of impregnating polyvinyl alkyl ether in the porous voids in the slider or coating the voids with the same substance, and Japanese Patent Application Laid-open No. 169,264/81 a method of impregnating fluorine polymer, alkyl ester or the like in the voids.
All of the proposals intend to apply impregnation or coating of the highly lubricative materials to the air bearing surface of the slider and are surely successful from the standpoint of improving the slidability. However, if the lubricant is coated to an appreciable thickness which is sufficient to meet only the requirement for slidability, then the effective gap between the slider and the recording medium will be decreased, adversely affecting the sliding operation. To obviate this inconvenience, if the gap is increased, this expanded gap between the magnetic head and the recording medium will have an adverse effect on the magnetic recording operation. If, for elimination of this disadvantage, a thin coating is applied, then its effect will be nullified rapidly, resulting in impairment of the promising improvement of the slidability. With the impregnation of the lubricant in the porous voids in the slider, an improvement in the slidability is expected on the one hand but it happens on the other hand that the head adheres to the recording medium. This phenomenon is observed in a disc device of the contact-start-stop type. For example, when the disc device continues to stop operating for about half a day, lubricants impregnated in large size voids ooze out, on account of their surface tension, to occupy a gap between the head and the recording medium, thereby causing the adhesion phenomenon. In order to prevent this adhesion phenomenon, not only the number and size of the porous voids in the slider must be controlled purposely but also the viscosity and quantity of the liquid lubricant must be selected. To this end, an extremely sophisticated technique is required.